The invention relates to a gas flow regulating device for cleaning a particulate filter. The invention also relates to an arrangement for cleaning a particulate filter comprising such a device, and to a method for cleaning a particulate filter using such a device.
A diesel particulate filter (DPF) removes organic and inorganic particulate matter (PM) from the exhaust gas stream of an engine. The organic particulate is a complex blend of carbon, hydrogen and oxygen, and is a result of incomplete combustion of the diesel fuel in the cylinder. The inorganic portion of the PM has its source in the additives in the lubrication oil or fuel, and material eroded from the engine surfaces. A large part of these inorganic substances consist of metal sulphur oxides, for example calcium sulphate. This means they will permanently clog the particulate filters in the long run. Under optimal circumstances, the organic PM will fully combust during filter regeneration and thus leave the filter as gaseous CO2 and H2O. The inorganic component, on the other hand, can not be oxidized inside the filter and converted to gaseous components. Instead it is trapped in the filter as various oxides, commonly termed “ash”. To maintain acceptable performance, the ash must be periodically removed from the filter to prevent it from clogging.
Some installations of diesel particulate filters (DPF) are made on engines which have operating temperatures too low to properly regenerate the filter, for instance, by oxidizing the organic PM. In these cases, the filter can become clogged with PM and potentially reduces the performance of the engine. In addition, a filter with a high soot load has a higher chance of permanent damage through uncontrolled regeneration than one with low soot load. In these cases of insufficiently high operating temperature, regular removal of the soot may be required.
Prior art approaches to filter cleaning, as discussed below, are often complex or comprise moving parts, while others are ineffective at removing tightly bound particulate matter. Other processes can lead to high PM emissions during the cleaning process.
The following examples illustrate a number of prior approaches (e.g., devices and methods) and their disadvantages.
I. Cleaning the DPF when Removed from the Engine
A simple way to clean a filter is with a compressed air hose. The hose is directed into the exit face of the filter, thus blowing the soot out of the wall in the reverse direction to which it was initially deposited (i.e., backwashing or back flushing). This method is imprecise, potentially dangerous (compressed air hazards), requires the full attention of an operator, and if improperly performed can lead to emission of PM from the filter end as well as a poorly cleaned filter.
The dirty filter can be heated in an oven to a high temperature in order to effectively remove the carbon-based particles. This requires a significant energy input and does not remove the inorganic ash. After a heating cycle, the cool down period is significant, and the ash must be removed through vacuuming or washing the filter.
Many systems for cleaning industrial devices utilize a combination of liquid flow and ultrasound, which may be effective, but can be comparatively expensive. In addition, the cleaning liquid can damage the catalytic coating or the matting material which secures the catalyst within its metal housing.
Other methods have described cleaning systems which involve backwashing with a suitable “cleaning fluid” until the filter is clean. However, many catalysts and their matting material are sensitive to large amounts of water or solvents. Solvents have the additional disadvantage of requiring disposal. In addition, the flow of cleaning fluid might not be controlled locally (i.e., a single fluid stream flows over the unit), so that some sections of the filter might not be cleaned as well as others.
A problem with such solution is that all garages or service facilities may not have suitable equipment for filter cleaning. In this case the vehicle may need to be fitted with a replacement filter to remain in operation while the filter is being cleaned. This requires a store of relatively expensive filters to be maintained by the garage or haulage company, in order to have access to replacement filters at all times.
II. Cleaning the DPF while Mounted on the Engine
Methods for collecting particulate using several particulate filters with valves to control the flow path are described in a number of patent documents.
For instance, U.S. Pat. No. 5,930,994 shows a combination of valve settings can start the back-flush of one of the filters i.e., the direction of gas flow is reversed and flows to push the soot out of the filter. The reversed gas flow can be heated to allow soot to be burned off as the air passes the DPF.
U.S. Pat. No. 5,725,618 discloses a method which ‘backwashes’ a DPF to remove the particulate and ash collected in the filter. The backwashing occurs while the device is on the vehicle, and an impact air valve is used to provide a pressure wave to dislodge the particulate matter. In order to allow the entire DPF to be cleaned, the filter unit is rotated in order to expose a predetermined sector of the filter unit to the air stream supplied by the impact air valve.
The above “back-flush” methods have the disadvantage that the ash from the lubricating oil never leaves the filter system, as back-flushed ash from one element flows into another element, and manual cleaning will still be required. Also, the dislodged material must somehow be removed from the exhaust conduit receiving said material.
JP3253712 and WO2012/041455 disclose valve and gas channel arrangements for reversing the exhaust gas flow through the filter and propose the use of this flow for cleaning. These arrangements are, however, rather difficult to apply in practice because the additional gas channels require additional space and reduce the gas flow velocity which may become too low for efficient cleaning.
III. Rotating Arms
A further method of cleaning a DPF involves a device using a rotating electrical heating element. A portion of the exhaust gas bleeds through a rotating arm and flows over the heating element. The combination of low flow rate and high temperature improves the chance of regeneration.
U.S. Pat. No. 5,116,395 discloses a dust collector with on-board programmable cleaning control. A rotating arm with a plurality of nozzles mounted upon it provides the back-flushing flow, thus causing the particulate to be removed from the bag surface and settle into a collection chamber. The control system operates the arm and nozzles to produce jets of cleaning fluid above the various bag units. The arm also contains a sensor for determining the dirtiness of each filter element (a pitot tube is suggested). The system described in the patent has several design elements which make it unsuitable for use in diesel particulate filter applications. First, DPFs are much smaller than dust collectors, and the nozzle designs in the above dust collector are specialized for large filters. A typical DPF is between 15 cm and 32 cm in diameter. The dust collector shown in the patent appears have a relatively large diameter. Second, DPFs can have many thousand cells, and thus focusing air on each individual cell is impractical. Other similar designs for dust collectors have the same shortcomings.
It is desirable to provide solutions for achieving an sufficient cleaning of a vehicle particle filter in a cost-efficient way.
According to a first aspect, a gas flow regulating device for cleaning a particulate filter is provided, said device being configured to be arranged in connection to the filter at a side thereof in a through-flow of a gas to be used for cleaning the filter. The inventive device is characterized in that it is a standalone unit configured to be removably installed in connection with a cleaning process. The device comprises a frame defining a gas flow passage and a gas flow regulating element arranged inside the frame, wherein the gas flow regulating element is provided with an opening structure comprising at least one opening for gas through-flow and a blocking part capable of blocking a portion of a gas through-flow area of the filter such as to force the gas to flow through the at least one opening, wherein the gas flow regulating element is movably arranged between at least two different positions, and wherein the opening structure covers different portions of the gas through-flow area in said different positions.
The inventive device is thus a form of adapter intended to be connected to the filter during cleaning and disconnected when the cleaning is completed. Typically, the device is kept at a service facility where the cleaning process is to be performed. When the device is connected to the filter it forces the gas flow to pass through a smaller area, i.e. through the at least one opening, which increases the velocity of the gas flow. This accelerated gas flow will pass through only a portion of the parallel gas channels normally arranged in a particulate filter. Due to the increased speed of the cleaning gas flow, the cleaning process will be more efficient. By moving the gas flow regulating element between the at least two positions, either stepwise or continuously, and thus block some cleaned gas channels and expose some other non-cleaned channels from/to the cleaning gas flow, the entire filter can be cleaned portion by portion in an efficient manner.
Such an adapter may be used by an operator/owner of the vehicle and/or a service station for the cleaning. The adapter is cost-efficient in production and requires no specific design solutions on the particulate filter or the exhaust system, which creates conditions for a cost efficient solution.
The side of the filter intended to form an inlet side for the gas flow to be used for cleaning preferably forms the outlet side of the filter during its normal operation. This way a “back-flush” effect is achieved during cleaning. The gas flow regulating device is preferably arranged on the side of the filter forming the inlet side during cleaning.
The inventive device is primarily intended for applications where an exhaust gas flow is used for cleaning but can be used also for other cleaning gas flows, such as an air flow.
Typically, the inventive device is intended for applications where the device is connected to a particulate filter that has been removed from its normal operational position prior to cleaning. However, the inventive device can be connected to a filter that is to be cleaned while remaining in its normal operational position.
In an embodiment of the invention the gas flow regulating element is arranged in a turnable manner around an axis that is substantially parallel with an intended gas flow direction in the gas flow passage defined by the outer frame. Thus, the gas flow regulating element can form a plate extending in a plane perpendicular to the direction of the gas flow. Preferably, the gas flow regulating element is configured for a stepwise or continuous turning such that, when the gas flow regulating element has been turned 360 degrees, the at least one opening has covered the entire gas through flow area of the filter.
According to a further embodiment, the frame comprises a first flange for connection to the particulate filter during the cleaning process. A flange is cost efficient to achieve on the frame, for example in the case the frame is formed by a tubular sheet, the flange may be achieved by bending a free end of the sheet radially outwards. Alternatively, the flange may be achieved by rigidly attaching a separate element to the outer surface of the frame, for example by welding or soldering. Preferably, the first flange has the shape of a radially projecting portion from the frame, especially of a relatively thin design, such as a single sheet. Further, preferably, the first flange is preferably inclined in a manner commensurate with the shape of the contacting surface of the particulate filter flange so that it may be firmly connected to the particulate filter flange, such as via clamping.
According to a further embodiment, the first flange has a shape configured for attachment to a flange of the particulate filter, which is configured for attachment of the particulate filter to a gas supplying unit in an operative position of the filter, for attachment of the gas flow regulating device to the particulate filter flange via said first flange. Preferably, the first flange has the shape of a radially projecting portion from the frame, especially of a relatively thin design, such as a single sheet. Further, preferably, the first flange is preferably inclined in a manner commensurate with the shape of the contacting surface of the particulate filter flange so that it may be firmly connected to the particulate filter flange, such as via clamping via a V-shaped clamping band/ring or similar.
Preferably, the first flange is positioned in the vicinity of a first end surface of the gas flow regulating device in an intended gas flow direction.
According to a further embodiment, the frame comprises a second flange for connection to a gas supplying unit capable of providing said through-flow of gas. Thus, the gas flow regulating device may be firmly connected to the gas supplying unit, which may be a component of an exhaust system of the internal combustion engine, via said second flange.
According to a further embodiment, the second flange has an at least substantially similar shape as a flange of the particulate filter, which is configured for an attachment of the particulate filter to the gas supplying unit in an operative position of the filter, for attaching the flow regulating device to the gas supplying unit flange via the second flange. This embodiment creates conditions for using the same connection means of the gas supplying unit for the filter attachment during ordinary operation as for connection of the gas flow regulating device during cleaning. Thus, no specific design of the gas supplying unit is required.
Further, the second flange may be formed by a bent sheet, which is rigidly attached to the frame via welding or soldering. The bent sheet may comprise two cylindrical contact surfaces at an axial distance from each other and an intermediate portion forming a loop in the form of a U-shape or V-shape or similar in cross section.
Preferably, the second flange is positioned in the vicinity of a second end surface of the gas flow regulating device in an intended gas flow direction. Preferably, the second flange is positioned at a sufficient distance from the closest end surface of the gas flow regulating device for achieving a support of an axially projecting portion of the frame past the second flange to an interior surface of the gas supplying unit. Especially, the first flange is positioned at an axial distance from the second flange.
The design of the gas flow regulating device with the first and second flange creates conditions for arranging the gas flow regulating device in a position between the gas supplying unit and the particulate filter for the cleaning operation. More specifically, the particulate filter would first be removed from the gas supplying unit, the gas flow regulating device attached to the flange of the gas supplying unit via the second flange and to the particulate filter via the first flange, wherein the gas flow regulating device would form an intermediate member creating a distance between the gas supplying unit and the particulate filter during the cleaning operation.
Preferably, the first and/or second flange extends in a continuous manner around the entire frame. Alternatively, the first and/or second flange extends in a discontinuous manner around the frame.
According to a second aspect, an arrangement is provided for cleaning a particulate filter comprising a device of the above type, a particulate filter, wherein the gas flow regulating device is connectable to the filter at a side thereof intended to form an inlet side for a gas flow to be used for cleaning the filter.
According to a third aspect, a method is provided for cleaning a particulate filter, comprising the steps of: connecting a gas flow regulating device of the above type to a particulate filter at a side thereof for through-flow of a gas to be used for cleaning the filter; and supplying a flow of cleaning gas to the gas flow regulating device and the particulate filter.
According to one embodiment, the particulate filter is mounted in an operative position attached to a gas supplying unit under normal operation of said engine, the method further comprising the steps of:                disassembling and removing the particulate filter from the gas supplying unit;        attaching the gas flow regulating device to the gas supplying unit,        reassembling the particulate filter in a reversed position to the gas flow regulating device before supplying the flow of cleaning gas.        